P0391
UniversalCamshaft Position Sensor B Circuit Range/Performance (Bank 2)
Medium SeverityThe P0391 code indicates a problem with the signal range or performance of the Camshaft Position Sensor B on engine Bank 2. This issue can disrupt the engine's ability to accurately time fuel injection and ignition, potentially leading to noticeable performance problems or preventing the vehicle from starting.
⚠️ Before You Begin (Safety First)
Always wear appropriate personal protective equipment, such as safety glasses and gloves, when working on your vehicle. Ensure the engine is cool before touching components and disconnect the battery before performing any electrical work to prevent accidental shocks or damage to the electrical system.
Common Symptoms
- Engine cranks but won't start
- Hard starting
- Rough idle
- Reduced engine power
- Engine stalling
- Check Engine Light illuminated
Common Causes
- Faulty Camshaft Position Sensor B
- Damaged, frayed, or corroded wiring to the sensor
- Poor electrical connection at the sensor or PCM
- Incorrect sensor installation
- Rarely, a faulty Powertrain Control Module (PCM)
Frequently reported on: Ford F-150 (2004-2010), Nissan Altima (2002-2006), Chevrolet Silverado (2007-2013), Honda Odyssey (2005-2010)
Diagnostic Steps
- Locate Camshaft Position Sensor B on Bank 2 of your engine (refer to a service manual for exact location).
- Visually inspect the sensor and its electrical connector for any signs of damage, corrosion, or loose connections.
- Check the sensor's wiring harness for any frayed, cut, or shorted wires.
- If accessible, test the sensor's resistance and output voltage using a multimeter according to manufacturer specifications.
- If tests indicate a fault, replace the sensor, ensuring proper alignment and connection.
- Clear the trouble code using an OBD-II scanner and test drive the vehicle.
👨🔧 When to Call a Professional
If after inspecting the sensor and wiring, the code persists, or if you suspect a deeper electrical issue or internal engine problem, it's best to consult a professional mechanic. Advanced diagnostics are often required for intermittent electrical issues or PCM-related faults.
Commonly Asked Questions
What does Bank 2 mean?
Bank 2 refers to the side of the engine that does not contain cylinder #1. This typically applies to V-type engines (V6, V8, etc.).
Can I drive with a P0391 code?
While possible, it is not recommended. The engine's performance may be severely compromised, leading to stalling or inability to start, especially in critical situations.
Is diagnosing P0391 difficult?
Diagnosing P0391 can range from easy (simple sensor replacement) to advanced (tracing intermittent wiring faults or PCM issues). Basic sensor inspection and replacement are usually manageable for DIYers.
What's the difference between 'circuit range' and 'performance'?
'Circuit range' suggests the sensor's signal is outside expected voltage parameters, while 'performance' indicates the signal is erratic or not consistent with engine operation, even if within voltage range.